N-heterocyclic-N-(4-piperidyl)amides and pharmaceutical compositions and their use as analgesics

ABSTRACT

N-heterocyclic-4-piperidiyl-amides as analgesics and antagonists of opioids with respect to such undesirable side effects as respiratory depression. 
     Exemplary compounds have the formula ##STR1## in which formula R is a heterocyclic group, and R 1  is a furanyl, thienyl, or lower alkoxy lower alkyl group, and R 2  is a lower alkyl phenyl group.

This is a divisional application of Ser. No. 07/009,857, filed 2/2/87,now U.S. Pat. No. 4,791,112.

The present invention relates to a class ofN-heterocyclic-N-(4-piperidyl)-amides, and methods and compositionsemploying such compounds.

A number of patents disclose certainN-heterocyclic-N-(4-piperidyl)amides having therapeutic activity. Forexample, U.S. Pat. No. 4,546,105 to Effland et al. disclosespyrrolylamidopiperidines useful for the alleviation of pain. An articleentitled "Synthesis and Analgesic Activity of Derivatives of Fentanyl"by Zhu Youcheng et al, printed in Acta Pharmaceutica Sinica, Vol. XVI,No. 3, March 1981 (pp 199-209) discloses various N-heterocyclicsubstituted amidopiperidines which possess morphine-like effects. SigmarGrossmann Urich Moser and Ernest Mutschler, in Arch. Pharm. (Weinheim)311, 1010-1015 (1978) disclose various pyridine analogues of fentanylpossessing analgesic activity. Frans Janssens et al., in Journal ofMedicinal Chemistry, Vol. 28, No. 12, 1934-1947 (1985) disclose variousN-heterocyclic-4-piperidinamides possessing antihistaminic properties.

BACKGROUND OF THE INVENTION

Antagonists in general possess the property of reversing a previouslyadministered drug (the agonist). For example, the antagonist naloxone iswell known for use in reversing selected properties of narcoticagonists. Antagonists of narcotics are believed to function by bindingcompetitively to opioid receptors, thereby preventing occupation of theagonist. At least four types of opioid receptors have been identified inthe central nervous system: mu, kappa, sigma, and delta. The affinity ofa particular antagonist for each receptor may not be equal. However,antagonist compounds may act centrally or peripherally, at specificopiate receptors, through a non-specific analeptic mechanism, or througha neurotransmitter system. The full understanding of the complex affectsof antagonists must await the elucidation of opioid physiology.

The prior art antagonist compound naloxone has gained widespread use inanesthesia for the purpose of antagonizing opioid induced respiratorydepression and sedation, (Editorial, British Journal of Anesthesia, Vol.57, No. 6, June 1985, pp 547-549). The use of naloxone in the presenceof unwanted opioid effects has predominantly occurred in the immediatepost operative period.

Recent information has supported the need for caution in the use ofnaloxone. This need for caution is based on reports of unwanted sideeffects of naloxone itself, including ventricular dysrhythmia,hypertension and pulmonary oedema following intravenous administration.Another disadvantage of naloxone as an antagonist is that naloxone tendsto also reverse or antagonize the analgesic component of opioids.

There is therefore a need for a safe antagonist of opioid agonists whichwill selectively antagonize respiratory depression without theundesirable side effects of naloxone and which preferably does notantagonize the analgesia component of the opioid agonists.

SUMMARY OF THE INVENTION

Compounds of the present invention possess agonist-antagonistproperties. The antagonist effect of the present compounds causesreversal of the actions of analgesics and anesthetics, for example,respiratory depression or cardiovascular depression. The preferredcompounds of the present invention selectively reverse respiratorydepression of narcotic or opiate analgesics without reversal ofanalgesia at that dose. Agonist-antagonists of this class of compoundsare useful for post-operative pain control where respiratory depressionbut not analgesia must be reversed. Such compounds may be usedpre-operatively or intra-operatively, including as a supplement togeneral anesthesia.

The agonist effect of the present compounds causes analgesia, decreasedawareness of sensation and increases pain threshold. Preferred compoundsof the present invention exhibit comparatively low cardio-respiratoryadverse effects. At higher doses, compounds of the present inventionproduce sedation, loss of righting reflex, hypnosis and loss ofconsciousness.

It has now been found that very desirable agonist-antagonist propertiesare provided by compounds of the formula: ##STR2## optically activeisomeric forms thereof, and/or pharmaceutically acceptable acid additionsalts thereof. In the Formula (I) above, R is a saturated or unsaturatedheterocyclic ring system of 4 to 10 cyclic member atoms, including 1 to3 nitrogen atoms, and 0 to 1 sulfur or oxygen atoms, said heterocyclicring system either substituted or unsubstituted by lower alkyl, halogen,lower alkoxy, halogenated lower alkyl, lower alkylthio or combinationsthereof; R₁ is a furanyl or thienyl group or a lower alkoxy lower alkylgroup; and R² is a phenyl lower alkyl group.

A preferred class of compounds within the scope of the present inventionare of the formula ##STR3## optically active isomeric forms thereof,and/or pharmaceutically acceptable acid addition salts thereof, in whichformula: R is a substituent selected from the group consisting ofpyrrolyl, piperidyl, pyrazyl, morpholyl, pyridyl, pyrimidyl, triazolyl,indazolyl, indolyl, quinolyl, benzoxazolyl, benzisoxazolyl,benzothiazolyl, benzisothiazolyl, or benzothiadiazolyl, all of which maybe unsubstituted or substituted with halogen, lower alkyl orcombinations thereof; R¹ is furanyl or thienyl, or a lower alkoxy alkylof 2-6 carbon atoms; and R² is phenyl lower alkyl.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, the compounds of the invention have the formula ##STR4##wherein R, R¹, and R², are as defined above. The compounds can be in theform of pharmaceutically acceptable acid addition salts, optionallyactive isomers, and/or cis/trans isomers thereof.

The group R in Formula I above is a heterocyclic ring system of 4 to 10cyclic member atoms containing 1 to 3 nitrogen atoms and 0 to 1 oxygenor sulfur atoms. Preferred heterocyclic rings are selected from thegroup consisting of pyrrolyl, piperidyl, pyrazyl, morpholyl, pyridyl,pyrimidyl, triazolyl, indazolyl, indolyl, quinolyl, benzoxazolyl,benzisoxazolyl, benzothiazolyl, benzisothiazolyl, benzothiadiazolyl, theforegoing rings either unsubstituted or substituted, wherein thesubstituents are selected from the group consisting of halogen(preferably chlorine or fluorine), lower alkyl, lower alkoxy,halogenated lower alkyl, lower alkylthio or combinations thereof.

Suitable R groups include 1-pyrrolyl, 1,2,4-triazol-4-yl, 1-piperidyl,4-morpholyl, 2-pyridyl, 4-methyl-2-pyridyl, 3-pyridyl, 4-pyridyl,2-chloro-3-pyridyl, 2-chloro-5-pyridyl, 2-pyrimidyl, 2-pyrazyl,2-chloro-4-pyrimidyl, 6-chloro-4-pyrimidyl, 4-chloro-6-pyrimidyl,1,3-benzoxazol-2-yl, 1,3-benzothiazol-2-yl, 2,1,3-benzothia-diazol-4-yl,1H-indazol-5-yl, 3-quinolyl, 1H-indol-5-yl, 2,1-benzisothiazol-3-yl,1,2-benzisoxazol-3-yl, 5-chloro-1,2-benzisoxazol-3-yl,1,2-benzisothiazol-3-yl. Preferred R groups are 4-methyl-2-pyridyl,2-pyrazol, 2-chloro-3-pyridyl, and 2,1,3-benzothiadiazol-4-yl,1-piperidyl, 2-pyrimidyl, 3-pyridyl, 2-chloro-4-pyrimidyl, and4-chloro-6-primidyl.

The group R¹ in Formula I above is a furanyl or thienyl group, or alower alkoxy lower alkyl. The furanyl or thienyl group is preferablyattached to the carbonyl carbon at the 2 or 3 position of the ring.Example of suitable R¹ groups include methoxymethyl, ethoxymethyl,1-propoxymethyl, 2-propoxymethyl, 1-butoxymethyl, 1-pentoxymethyl,1-hexoxymethyl, 1-heptoxymethyl, 1-heptoxy-methyl, 1-methoxyethyl,1-ethoxy-1-ethyl, 1-butoxy-1-ethyl, 2-furanyl, 3-furanyl, 2-thienyl, or3-thienyl. A preferred R¹ group is 2-furanyl or 3-furanyl.

R² in Formula I above is a phenyl lower-alkyl. Suitable R² groupsinclude 2-phenylethyl, 1-phenyl-2-propyl, and 2-phenyl-1-propyl.

By lower-alkyl or lower alkoxy groups, we mean branched or unbranchedgroups containing from 1 to 7 carbon atoms.

The compounds of the invention can exist in the form of the free base orthe therapeutically or pharmaceutically acceptable acid addition saltsby treatment with an appropriate acid, such as an inorganic acid, e.g.,hydrochloric, hydrobromic, sulfuric, nitric, phosphoric acids and thelike; or an organic acid such as acetic, trifluoroacetic, propionic,hydroxyacetic, methoxyacetic, benzoic, citric, oxalic, methanesulfonic,ethanesulfonic, benzenesulfonic, toluenesulfonic, succinic, tartaric,and the like acids. Preferred acid addition salts are the chloride,oxalate or citrate. These acid addition salts can be prepared byconventional methods, e.g., by treatment with the appropriate acid.

Compounds of the invention having at least one assymetric carbon atomcan exist in optically active isomeric forms. For example, in compoundsin which R² is a 2-phenyl-1-propyl or 1-phenyl-2-propyl group, etc., thecarbon adjacent to the piperidinyl nitrogen is an assymetric carbon andsuch compounds can therefore exist in optical active isomeric(enantiomeric) forms. Such isomeric forms can be isolated from theracemic mixtures by techniques known to those skilled in the art.

The compounds of the invention, prepared as the free base, can becombined with a pharmaceutically acceptable carrier to provide apharmaceutical composition. Suitable carriers for the free bases includepropylene glycol-alcohol-water, isotonic water, sterile water forinjection, USP, emulphor ™-alcohol-water, cremophor-EL™ or othercarriers known to those skilled in the art.

The compounds of the invention prepared as the pharmaceuticallyacceptable acid addition salts can also be combined with apharmaceutically acceptable carrier to provide a pharmaceuticalcomposition. Suitable carriers for the acid addition salts may includean isotonic aqueous solution, or sterile water for injection, USP, aloneor in combination with other solubilizing agents such as ethanol,propylene glycol, or other conventional solubilizing agents known tothose skilled in the art. Of course, the carrier will vary dependingupon the mode of administration desired for the pharmaceuticalcomposition as is conventional in the art. A preferred carrier is anisotonic aqueous solution containing from 0.01 to 4.0 mg/ml of at leastone of the compounds of this invention depending upon the pharmacologyof the individual compounds being employed in the formulation.

The compounds of the invention can be administered to mammals, e.g.,animals or humans, in amounts effective to provide the desiredtherapeutic effect. The compounds can be administered intravenously,intramuscularly or subcutaneously in the previously described carriers.These compounds may also be administered orally, sublingually, rectally,or transcutaneously with a suitable pharmaceutically acceptable carrierfor that mode of administration as is conventional in the art.

As noted above, an effective amount of the compounds of the presentinvention is employed to obtain the desired therapeutic effect. Sincethe activity of the compounds and the depth of the desired therapeuticeffect vary, the dosage level employed of the compound also varies. Theactual dosage administered will be determined by such generallyrecognized factors as the body weight of the patient or theidiosyncrasies of the particular patient. Thus, the unit dosage for aparticular patient (man) could be as low as 0.30 mg/Kg, which thepractitioner may titrate to the desired effect.

The compounds of the present invention can be prepared by variousmethods. In general, the desired compounds of Formula I above can beprepared by reacting a compound of the formula ##STR5## with a compoundof the formula ##STR6## or by reacting a compound of the formula##STR7## with a compound of the formula

    R.sup.2 X

wherein R, R¹, R², R³ and R⁴ have the meanings given above and Xrepresents halide or its reactive equivalent.

Several convenient routes for the preparation of the compounds of theinvention begin with known piperidones as shown below: ##STR8## Thecompound 4-(2-phenylethyl)-piperidone can be prepared according to theprocedure published by A. H. Becket, A. F. Casey and G. Kirk, J. MedPharm. Chem., Vol. 1, 37 (1959). The compound 4-benzyl-1-piperidone canbe prepared in an analogous manner by the procedures described by C. R.Ganellin and R. G. Spickch, J. Med. Chem., Vol. 8, 619 (1965) or P. M.Carabateas and L. Grumbach, J. Med. Pharm. Chem., Vol. 5, 913(1962).

In one example of a process of the invention, 4-benzyl or4-(2-phenylethyl)-piperidone may be reacted with a heterocyclic amine ora substituted heterocyclic amine and the resulting Schiff base may bereduced with, for example, sodium borohydride to give 1-benzyl or1-(2-phenylethyl)-4-heterocyclic-aminopiperidine or the correspondingsubstituted heterocyclic compound if the substituted heterocyclic amineis used. See for example, Grossman, S. et al., Arch. Pharm. (Weinheim)311, 1010 (1978). The following reaction scheme, wherein R represents aheterocyclic group according to the present invention, illustrates sucha method: ##STR9##

The latter compound can be reacted with the appropriate acid halide(e.g., R¹ (COCl) or anhydride [(R¹ CO)₂ 0] to introduce the appropriateR¹ --CO-- group into the amino nitrogen.

A second method for the preparation of the compounds of the inventionutilizes the intermediate, 4 amino-1-R² -piperidine, for example,4-amino-1-phenethyl piperidine. This method employs an aromaticnucleophilic substitution to obtain a secondary amino precursor foracylation. See, for example, Zhu, Y. et al, Acta Pharm Sinica, 16, 199(1981). The following reaction scheme, where R represents a heterocyclicgroup according to the present invention, illustrates such a method:##STR10##

A third method for the preparation of compounds of the present inventionalso utilizes the intermediate 4-amino-1-R-piperidine, for example,4-amino-1-phenylethyl piperidine. In this regard, see Langhein, et al.,Offenlegungschrift, 234 1965 (1975); Chem. Abstr. 82, 156121W (1975).

This method involves reacting an oxo derivative of the heterocycle Rwith said intermediate to form a secondary amine which is reduced priorto acylation. The following reaction scheme illustrates such a method:##STR11##

Finally, selective aromatic N-oxidation with meta-chloroperoxybenzoicacid of compounds of the present invention having pyridyl heterocyclicgroups thereby yields desired N-oxide analogues.

The following examples are presented for purposes of demonstrating, butnot limiting the compounds or compositions of this invention.

EXAMPLE I

An oxime intermediate was prepared as follows: Prior to use,N-(phenylethyl) piperidone was recrystallized from hexane in a 2000 mlbeaker. 50 g (0.246 mol) of N-(phenylethyl) piperidone was dissolved in200 ml of ethanol with necessary heat. This solution was added to a warmsolution of 34.2 g (0.492 mol) of hydroxylamine hydrochloride and 200 mlof deionized water. An additional 500 ml of water was added to dissolvethe phenylethylpiperidone oxime hydrochloride which began a precipitate.Solid NaHCO₃ (41.3 g, 0.492 mol) was added portionwise. The mixture wasthen heated to nearly boiling and set aside to cool to room temperature.Enough ice to fill a 1000 ml beaker was added and the mixture wasstirred overnight. The solid product was filtered, washed with water(5×200 ml), and dried in vacuo. The crude oxime (52 g, 97%, mp132°-133°) was sufficiently pure for use in the next reaction. Ananalytically pure sample (mp 132.5°-134.5° ) of the following compoundwas obtained by recrystallization from 95% ethanol.

    ______________________________________                                                    Calcd  Found                                                      ______________________________________                                        C             71.52    71.76                                                  H             8.31     8.23                                                   N             12.84    13.04                                                   ##STR12##                                                                    ______________________________________                                    

EXAMPLE II

The oxime of Example I was reduced as follows. Prior to use,tetrahydrofuran was dried by distillation from LiAlH₄ followed bystorage over 3A molecular sievers. To a stirring suspension of 8.7 g(0.23 mol) of LiAlH₄ in 100 ml of dry tetrahydrofuran (THF), was addeddropwise (at such a rate so as to maintain a brisk reflux) a solution of50 g (0.23 mol) of oxime from Example I in 400 ml of THF. On completionof addition, the reaction mixture was heated under reflux overnight. Theheating mantle was carefully replaced with a ice-water bath. Quenching,to liberate the basic product, consisted of successive additions of 8.7ml of H₂ O, 8.7 ml of 15% NaOH, and 26.1 ml of H₂ O. The insolublematerial was filtered, washed with THF (3×200 ml), and the combinedfiltrates concentrated in vacuo. The residual oil was dissolved in CH₂Cl₂ (300 ml), washed with water (2×100 ml), and dried over Na₂ SO₄.Vacuum distillation of the crude oil, left after evaporation of solvent,gave a colorless product [35 g, 74%, bp 142° (0.10 mm Hg)]. The storagecontainer was tightly capped and placed in a dessicator at this stronglybasic amine forms salts of atmospheric carbon dioxide (H₂ CO₃). Ananalytically pure sample of the following compound was obtained as thedihydrogen oxalate hemihydrate from i-PrOH-H₂ O (mp 191°-192°).

    ______________________________________                                                    Calcd  Found                                                      ______________________________________                                        C             51.90    51.58                                                  H             6.41     6.21                                                   N             7.12     7.11                                                    ##STR13##                                                                    ______________________________________                                    

EXAMPLE III

This example illustrates the preparation of an RX reagent, asgenerically defined supra, for reaction with the intermediate of ExampleII. The starting material 2-amino-4-picoline is commercially availablefrom Aldrich. To an ice-chilled solution of 50 g (0.46 mol) of2-amino-4-picoline, 250 ml of concentrated HCl and 150 ml of water wasadded, dropwise, a solution of NaNO₂ (32 g, 0.46 mol) in 150 ml of water(maintaining an internal temperature of between 0° and 3°). Afteraddition of NaNO₂, the reaction mixture was stirred for 45 min. and then120 ml of ice cold concentrated NH₄ OH was added. A yellow suspensionwas extracted with chloroform (2×400 ml). This organic extract waswashed with water (500 ml), brine (200 ml), and dried over Na₂ SO₄.Concentration in vacuo left a green oil which was distilled (100°-110°,30 mm Hg) to yield the product as a colorless oil (16 g, 27%) having thefollowing structure: ##STR14##

EXAMPLE IV

This example illustrates the further preparation of an RX reagent, asgenerically defined supra, for reaction with the intermediate of ExampleII. Under reflux, a mixture of 16 g (0.125 mol) of the product ofExample III, 27 g (0.125 mol, 80%) of 3-chloroperbenzoic acid, andchloroform (250 ml) was stirred. After 4 hr. the mixture was cooled andpartially concentrated to precipitate benzoic acid. The suspension wasfiltered and the filtrate washed with 6N NaOH, water, brine, and driedover Na₂ SO₄. Purification by flash chromatography (400 g fine silica;CHCl₃ --MeOH--NH₃, 100:1:0.1) yielded 6.2 g (35%) of the product havingthe following structure as a red oil which was found to be homogenous byTLC (Rf 0.30; CHCl₃ --MeOH--NH₃, 95:5:0.5). ##STR15##

EXAMPLE V

This example illustrates the reaction of the intermediate of Example IVwith the intermediate of Example II. A mixture of 6.2 g (43 mmol) of theproduct of Example IV, 9.2 g (45 mmol) of the product of Example II, 23g anhydrous Na₂ CO₃, 200 mg of KI, and 150 ml of 3-methyl-1-butanol wasprepared. Under reflux the mixture was stirred for 48 hr. and thencooled and filtered. The filtrate was concentrated in vacuo. The residuewas partitioned between 10% HCl (100 ml) and ether (100 ml). The acidicaqueous phase was alkalinized with 12N NaOH and the liberated free basewas extracted with methylene chloride (2×100 ml). The organic extractwas washed with water (100 ml), brine (50 ml), and dried over Na₂ SO₄.Concentration in vacuo left a purple oil which was eluted through 650 gof fine silica with CHCl₃ --MeOH--NH₃ (20:1:0.1) to yield the followingproduct as a viscous, red oil (3.5 g, 26%) which was homogeneous by TLC(Rf 0.31; CHCl₃ --MeOH--NH₃, 95:5:0:5). ##STR16##

EXAMPLE VI

This example illustrates the reduction of the product of Example V. Toan ice-chilled solution of 3.5 g (11.2 mmol) of the product of Example Vin chloroform (80 ml) was added, dropwise, phosphorous trichloride (11.2ml) while maintaining an internal temperature of 0°. After this, thereaction mixture was stirred under reflux for 2 hr, cooled, and pouredinto a 1000 ml beaker of ice. The acidic mixture was cautiouslyalkalinized with 20% NaOH. The liberated free base was extracted withmethylene chloride (100 ml) and the organic extract washed with water(100 ml), brine (100 ml), and dried over Na₂ SO₄. Initial purificationby flash chromatography (120 g fine silica; CHCl₃ --MeOH--NH₃ ; 25:1:01)yielded 2.4 g of a tan solid which required further chromatography (aspreviously), finally yielding the following product as a pale yellowsolid (2.0 g, 61%). ##STR17##

EXAMPLE VII

This example illustrates the conversion of the product of Example VI toa compound according to the present invention. To a stirring mixture of0.94 g (3.2 mmol) of the product of Example VI, 1.0 ml of triethylamineand 8 ml of chloroform was added, with a disposable pipet, a solution of0.38 ml of 2-furoyl chloride in 2 ml of chloroform. The mixing wasmildly exothermic and after stirring at ambient temperature for 30 min,TLC analysis (CHCl₃ --MeOH--NH₃, 95:5:0.5) indicated consumption of thestarting material. The reaction mixture was partitioned between 10% HCl(50 ml) and ether (50 ml). The aqueous phase was further extracted withether and then alkalinized with 12N NaOH. The liberated free base wasextracted with methylene chloride (2×50 ml) and the organic extractwashed with water (50 ml), brine (50 ml), and dried over Na₂ SO₄.Purification by flash chromatography (60 g fine silica; CHCl₃--MeOH--NH₃, 30:1:0.1) gave a pale yellow solid (0.94 g, 75%). This wasmixed with 217 mg of oxalic acid in hot isopropyl alcohol. A few dropsof isopropyl ether induced the precipitation of a white powder (mp197°-198°) which was further purified from isopropyl ether-isopropylalcohol-methanol (to dissolve) yielding 787 mg of a white powder (mp198°-199.5°) having the structure shown below.

    ______________________________________                                                    Calcd  Found                                                      ______________________________________                                        C             65.12    64.80                                                  H             6.10     6.10                                                   N             8.76     8.76                                                    ##STR18##                                                                    ______________________________________                                    

A second compound according to the present invention is prepared asdescribed in the following two examples.

EXAMPLE VIII

An intermediate compound was prepared as follows. A mixture of 13 g (64mmol) of the product of Example II above, 3.6 g (32 mmol) ofchloropyrazine, and 2.0 g (32 mmol) of copper powder was stirred at170°-180° for 6 hr. On cooling, a green mixture solidified. The solidwas broken into chunks with a spatula and gradually churned into a thicksoup in 10% HCl (100 ml). This was filtered of insolubles and thefiltrate extracted with ether (50 ml). Alkalinization with 12N NaOHliberated the free base which was extracted with methylene chloride(2×50 ml). The organic extract was washed with water (50 ml), brine (50ml), and dried over Na₂ SO₄. The green solid left after evaporation ofsolvent was eluted through 600 g of fine silica. This requiredsuccessive passages of CHCl₃ --MeOH--NH₃ (4000 ml of 100:1:0.1, 1800 mlof 90:1:0.1, 1600 ml of 80:1:0.1, 4000 ml of 70:1:0.1) to yield 4.0 g(44%) of the following product as a beige solid. ##STR19##

EXAMPLE IX

A compound according to the present invention was prepared from theintermediate of Example VIII as follows. To a stirring mixture of theproduct of Example VIII (1.5 g, 5.3 mmol), 1.5 ml of triethylamine, and13 ml of chloroform was added, with a disposable pipet, 0.63 ml (6.4mmol) of 2-furoyl chloride in 2 ml of chloroform. This was stirred underreflux for 5 hr, then cooled and concentrated in vacuo. The residue waspartitioned between 10% HCl (50 ml) and ether (50 ml). The aqueous phasewas alkalinized with 12N NaOH and extracted with methylene chloride(2×50 ml). The organic extract was washed with water (50 ml), brine (30ml), and dried over Na₂ SO₄. Purification by flash chromatography (55 gfine silica; CHCl₃ --MeOH--NH₃, 30:1:0.1) gave a white solid (0.9 g,45%). The hydrogen oxalate salt was initially precipitated fromisopropyl alcohol and recrystallized from an isopropyl alcohol solution(containing the minimal amount of aqueous methanol required to dissolvesalt) to finally yield 690 mg of a crude powder (mp 206°-207°) anoxalate salt of the compound having the following structure:

    ______________________________________                                         ##STR20##                                                                                Calcd  Found                                                      ______________________________________                                        C             61.79    62.17                                                  H             5.62     5.61                                                   N             12.01    12.28                                                  ______________________________________                                    

The following three examples illustrate the preparation of anothercompound according to the present invention.

EXAMPLE X

An intermediate compound is prepared as follows. A mixture ofN-phenethylpiperidone (17.4 g, 85.6 mmol),4-amino-2,1,3-benzothiadiazole (15 g, 99.2 mmol), a few crystals ofp-toluenesulfonic acid, and 170 ml of toluene was refluxed for 4 days.This time period is required for collection of the theoretical quantityof water-by-product (1.54 ml) in a Dean-Stark trap. The reaction mixturewas cooled and concentrated in vacuo to give a reddish-brown oil whichexhibits a strong Schoff base adsorption band (C═N, 1665 cm⁻¹) byinfrared analysis. The structure of the compound was as follows:##STR21##

EXAMPLE XI

The intermediate of Example X was reduced as follows. To a solution ofthe product of Example X in 150 ml of methanol was added, portionwise,3.7 g (98 mmol) of NaBH₄. The reaction mixture was heated under refluxfor 2 hrs., cooled, and concentrated in vacuo. Water (100 ml) was addedfollowed by extraction with toluene (200 ml). The organic extract waswashed with water (2×100 ml) and dried over Na₂ SO₄. Concentration invacuo left 33.5 g of a dark brown oil which by infrared analysis wasdevoid of any Schiff base. This was purified by flash chromatography(800 g fine silica; hexane-ethyl acetate-triethylamine, 150:100:1)leaving a red oil which crystallized on standing at room-temperature.TLC analysis (hexane-ethyl acetate-triethylamine, 100:100:1) showed thisto be the derived product with a trace of4-amino-2,1,3-benzothiadiazole. A homogenous product was obtained byrecrystallization from hexane, yielding 8.8 g (30%) of golden needles(mp 85°-88° C.). An analytical sample was obtained from isopropylalcohol as the hydrogen oxalate salt (mp 189°-190° C.) having thefollowing structure:

    ______________________________________                                         ##STR22##                                                                                Calcd  Found                                                      ______________________________________                                        C             58.86    58.76                                                  H             5.66     5.70                                                   N             13.08    12.89                                                  ______________________________________                                    

EXAMPLE XII

A compound according to the present invention was prepared from theintermediate of Example XI as follows. A mixture of the heteroaniline(1.0 g, 2.95 mmol), 3-furoyl chloride (0.77 g, 5.90 mmol), triethylamine(2 ml), and toluene (10 ml) was refluxed for 3 hr. The reaction mixturewas concentrated in vacuo and partitioned between 10% HCl (50 ml) andether (50 ml). Extraction of the aqueous acidic layer with additionalether was performed followed by liberation of free bases with 12N NaOH.These were extracted with CH₂ Cl₂ (2×50 ml) and the combined organicextracts washed with water (50 ml), brine (30 ml), and dried over Na₂SO₄. The crude product left after evaporation of solvent was elutedthrough 80 g of fine silica with hexane-ethyl acetate-triethylamine(150:100:1; slow drip rate of 1 drop per 5 sec. overnight followed byair pressure the following morning) yielding 0.9 g of an amber gum. Thiswas mixed with 187 mg of oxalic acid hot isopropyl alcohol.Precipitation of the salt was effected with addition of isopropyl ether.recrystallization from isopropyl ether-isopropyl alcohol-methanol-wateryielded 673 mg of analytically pure product (mp. 191°-192° C.) havingthe following structure:

    ______________________________________                                         ##STR23##                                                                                Calcd  Found                                                      ______________________________________                                        C             59.76    59.65                                                  H             5.02     5.08                                                   N             10.72    10.52                                                  ______________________________________                                    

EXAMPLE XIII-XXII

Further examples of compounds within the scope of the present inventionwhich may also be prepared by procedures analogous to those describedabove include:

N-(1-pyrrolyl)-N-[1-(2-phenylethyl)-4-piperidyl]-2-furamide.

N-(1,2,4-triazolyl-4-yl)-N-[1-(2-phenylethyl)-4-piperidyl]-3-furamide.

N-(2,1-benzisothiazol-3-yl)-N-[1-(2-phenylethyl)-4-piperidyl-3-furamide

N-(1,2-benzisoxazol-3-yl)-N-[1-(2-phenyethyl)-4-piperidyl]-3-furamide.

N-[5-chloro-1,2-benzisoxazol-3-yl)-N-[1-(2-phenylethyl)-4-piperidyl]-3-furamide.

N-[1,2-benzisothiazol-3-yl)-N-[1-(2-phenylethyl)-4-piperidyl)-2-furamide.

N-[6-chloro-1,2-benzisoxazol-3-yl]-N-[1-(2-phenylethyl)-4-piperidyl)-2-furamide.

N-(4-methylpyridin-2-yl)-N-[1-(2-phenyethyl)-4-piperidyl]-2-thienylamide.

N-(pyrazin-2-yl)-N-[1-(2-phenyethyl)-4-piperidyl]-2-thienylamide.

N-(2-chloropyridin-3-yl)-N-[1-(2-phenyethyl)-4-piperidyl]-3-thienylamide.

EXAMPLE XXIII

A number of compounds in accordance with the present invention weretested for their analgesic and reversal properties. Specifically, theacid addition oxalate salts of the compounds tested in accordance withthe invention were dissolved in sterile water for injection, USP, toform a solution whose concentration varied from 0.00001 mg/ml to 5mg/ml. The solution was administered intravenously in a mouse tail vain.

The ED₅₀ values were obtained from the mouse hot plate analgesia test(58° C.) described in Domer, Floyd R., Animal Experiments inPharmacological Analysis, Charles C. Thomas, Springfield, 1971, p. 283ff. The compounds listed in Table 1 below were tested by this procedureand found to have the analgesic activities listed in Table 1.

The reversal characteristics with respect to morphine were investigatedin rabbits and categorized by an integer 0, 1, or 2, wherein the number0 indicated no reversal of morphine effects, the number 1 indicatedreversal of only morphine respiratory depression, and the number 2indicated reversal of both respiratory depression and analgesia. Thesymbol NA indicates the compound was not active as an anesthetic oranalgesic at less than 10 mg/kg.

                                      TABLE I                                     __________________________________________________________________________                                               ANALGESIC                                                                     ACTIVITY                                                                              REVERSAL                   COMPOUNDS                           M.P. °C.                                                                      ED.sub.50 MG/KG                                                                       CHARACTERISTICS            __________________________________________________________________________      N--(1-piperidyl)-N--[1-(2-phenyethyl)-4-piperidyl]-methoxy                                                      212-212.5                                                                            2.25    1                            acetamide                                                                     N--(1-piperidyl)-N--[1-(2-phenyethyl)-4-piperidyl]-2-furamide                                                   229-230                                                                              2.75    1                            N--(4-morpholyl)-N--[1-(2-phenylethyl)-4-piperidyl]-methoxy-                                                    180-181                                                                              NA      0                            acetamide                                                                     N--(4-morpholyl)-N--[1-(2-phenylethyl)-4-piperidyl]-2-furamide                                                  203.5-205.5                                                                          2.25    1                            N--(2-pyridyl)-N--[1-(2-phenyethyl)-4-piperidyl]-methoxyacetamide                                               197-199                                                                              0.455   0                            N--(2-pyridyl)-N--[1-(2-phenylethyl)-4-piperidyl]-2-furamide                                                    209-210.5                                                                            0.081   1                            N--(2-pyridyl)-N--[1-(2-phenylethyl)-4-piperidyl]-3-furamide                                                    198.5-201                                                                            0.8     1                            N--(3-pyridyl)-N--[1-(2-phenylethyl)-4-piperidyl]-2-thienamide                                                  208-209                                                                              2.5     2                            N--(2-pyridyl)-N--[1-(2-phenylethyl)-4-piperidyl]-2-thienamide                                                  215-217.50                                                                           1.0     1                          10.                                                                             N--(4-methyl-pyridin-2-yl)-N--[1-(2-phenyethyl)-4-piperidyl]-2-                                                 198-199                                                                              NA      2                            furamide                                                                      N--(3-pyridyl)-N--[1-(2-phenylethyl)-4-piperidyl]-2-furamide                                                    194-194.5                                                                            1.5     1                            N--(3-pyridyl)-N--[1-(2-phenylethyl)-4-piperidyl]-3-furamide                                                    191-192                                                                              0.69                                 N--(2-chloro-pyridin-3-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-                                                  149-151                                                                              3.9     0                            methoxyacetamide                                                              N--(2-chloro-pyridin-3-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-2-                                                177-179                                                                              5.2     2                            furamide                                                                      N--(2-chloro-pyridin-3-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-3-                                                118-123                                                                              7.5     1                            furamide                                                                      N--(2-chloro-pyridin-5-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-                                                  180-182                                                                              NA      1                            methoxyacetamide                                                              N--(2-chloro-pyridin-5-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-2-                                                213-214                                                                              2.8     1                            furamide                                                                      N--(2-chloro-pyridin-5-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-3-                                                191.5-192                                                                            7.5     1                            furamide                                                                      N--(2-pyrimidyl)-N--(2-phenylethyl-4-piperidyl]-                                                                188-190                                                                              1.7     1                            methoxyacetamide                                                            20.                                                                             N--(2-pyrimidyl)-N--[1-(2-phenylethyl-4-piperidyl]-2-furamide                                                   211-212                                                                              10.0    2                            N--(2-pyrimidyl)-N--[1-(2-phenylethyl-4-piperidyl]-3-furamide                                                   212-214.5                                                                            2.25    1                            N--(2-pyrazyl)-N--[1-(2-phenylethyl-4-piperidyl]-2-furamide                                                     206-207                                                                              2.25    1                            N--(2-pyrazyl)-N--[1-(2-phenylethyl-4-piperidyl]-3-furamide                                                     204.5-207.5                                                                          4.7     1                            N--(2-chloro-pyrimidin-4-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-                                                173-174.5                                                                            NA      1                            2-furamide                                                                    N--(2-chloro-pyrimidin-4-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-                                                177-178                                                                              2.25    1                            3-furamide                                                                    N--(4-chloro-pyrimidin-6-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-                                                163.5-164                                                                            NA      1                            methoxyacetamide                                                              N--(4-chloro-pyrimidin-6-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-                                                193-195                                                                              NA      2                            2-furamide                                                                    N--(4-chloro-pyrimidin-6-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-                                                185-186.5                                                                            NA      1                            3-furamide                                                                    N--(4-pyridyl)-N--[1-(2-phenylethyl)-4-piperidyl]-2-furamide                                                    181-183                                                                              1.7     2                          30.                                                                             N--(4-pyridyl)-N--[1-(2-phenylethyl)-4-piperidyl]-3-furamide                                                    192-195                                                                              2.75    2                            N--(1,3-benzoxazol-2-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-                                                    205-206.5                                                                            2.5     0                            methoxyacetamide                                                              N--(1,3-benzoxazol-2-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-2-                                                  210.5-211.5                                                                          2.5     1                            furamide                                                                      N--(1,3-benzoxazol-2-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-3-                                                  219-219.5                                                                            NA      1                            furamide                                                                      N--(1,3-benzothiazol-2-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-                                                  220- 222                                                                             1.95    0                            methoxyacetamide                                                              N--(1,3-benzothiazol-2-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-2-                                                226.5-227      1                            furamide                                                                      N--(1,3-benzothiazol-2-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-3-                                                232-232.5                                                                            NA      1                            furamide                                                                      N--(1H-indol-5-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-methoxy-                                                  139-180                                                                              10.0    0                            acetamide                                                                     N--(1H-indol-5-yl)-N--[1-(2-phenylethyl)-4-piperidyl]-methoxy-                                                  150-152                                                                              NA      0                            acetamide                                                                     N--(2,1,3-benzothiadiazol-4-yl)-N--[1-(2-phenylethyl)-4-                                                        176-178                                                                              1.85    0                            piperidyl]-methoxyacetamide                                                 40.                                                                             N--(2,1,3-benzothiadiazol-4-yl)-N--[1-(2-phenylethyl)-4-                                                        142-145                                                                              3.5     2                            piperidyl[-2-furamide                                                         N--(2,1,3-benzothiadiazol-4-yl)-N--[1-(2-phenylethyl)-4-                                                        191-192                                                                              2.25    1                            piperidyl]-3-furamide                                                         N--(3-quinolyl]-N--[1-(2-phenylethyl)-4-piperidyl]-2-furamide                                                   171.5-175                                                                            0.78    1                            N--(2-pyrazyl)-N--[1-(2-phenethyl)-4-piperidyl]-2-thienamide                                                    228-230                                                                              3.5     1                          __________________________________________________________________________

It will be understood that the embodiments described herein are merelyexemplary and that a person skilled in the art may make many variationsand modifications without departing from the spirit and scope of theinvention. All such modifications and variations are intended to beincluded within the scope of the invention as defined in the appendedclaims.

We claim:
 1. A compound having the formula ##STR24## optically activeisomeric forms, or pharmaceutically acceptable acid addition saltsthereof, in which formula: R is selected from the group consisting ofbenzoxazolyl, benzisoxazolyl, benzothiazolyl, benzisothiazolyl andbenzothiadazolyl groups which may be unsubstituted or substitutedwherein the substituents are selected from the group consisting ofhalogen, lower alkyl, lower alkoxy, halogenated lower alkyl, loweralkylthio or combinations thereof; R¹ is furanyl or thienyl or a loweralkoxy lower alkyl; and R² is a phenyl lower alkyl.
 2. A compoundaccording to claim 1, which isN-(2,1,3-benzothiadiazol-4-yl)-N-[1-(2-phenylethyl)-4-piperidyl]-3-furamide.3. A narocotic antagonistic or analgesic composition comprising anon-toxic pharmaceutically acceptable carrier and therapeuticallyeffective amount of a compound of the formula ##STR25## optically activeisomeric forms, or pharmaceutically acceptable acid addition saltsthereof, in which formula: R is selected from the group consisting ofbenzoxazolyl, benzisoxazolyl, benzothiazolyl, benzisothiazolyl andbenzothiadiazolyl groups which may be unsubstituted or substitutedwherein the substituents are selected from the group consisting ofhalogen, lower alkyl, lower alkoxy, halogenated lower alkyl, loweralkylthio or combinations thereof; R¹ is furanyl or thienyl or a loweralkoxy lower alkyl; and R² is a phenyl lower alkyl.
 4. A compositionaccording to claim 3, which comprisesN-(2,1,3-benzothiadiazol-4-yl)-N-[1-(2-phenylethyl)-4-piperidyl]-3-furamideas the active ingredient.
 5. A method for producing selective reversalof the actions of opiate analgesics, including respiratory depression,in a mammal comprising administering to such mammal an antagonisticallyeffective amount of a compound of the formula ##STR26## optically activeisomeric forms, or pharmaceutically acceptable acid addition saltsthereof, in which formula: R is selected from the group consisting ofbenzoxazolyl, benzisoxazolyl, benzothiazolyl, benzisothiazolyl andbenzothiadiazolyl groups which may be unsubstituted or substitutedwherein the substituents are selected from the group consisting ofhalogen, lower alkyl, lower alkoxy, halogenated lower alkyl, loweralkylthio or combinations thereof; R¹ is furanyl or thienyl or a loweralkoxy lower alkyl; and R² is a phenyl lower alkyl.
 6. A methodaccording to claim 5, which comprises administeringN-(2,1,3-benzothiadiazol-4-yl)-N-[1-(2-phenylethyl)-4-piperidyl]-3-furamide.